ATI Radeon HD 4890: The RV790 Unveiled

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Introduction and Specifications

As anyone remotely in tune with the tech sector can attest, the rivalry in the PC graphics card market between AMD / ATI and NVIDIA is as intense as ever. It used to be that one of the two companies would release a new product, only to have the other release a competing offering a few weeks, or maybe a few months later. But even in these gloomy economic times, AMD and NVIDIA continue to fight on and today both graphics giants are releasing new graphics cards aimed squarely at one another. Not a few weeks apart, but simultaneously on the very same day. Don't believe us? See here for our NVIDIA GeForce GTX 275 coverage.

AMD is rolling out the ATI Radeon HD 4890 today, technically a new graphics card, but one that borrows heavily from the previous generation. The Radeon HD 4890 is based on an updated variant of the popular RV770 GPU which powers Radeon HD 4850 and 4870 cards, dubbed the RV790. We've got some technical details regarding the RV790 GPU below and have more particulars regarding the actual cards and performance on the pages ahead. Read on to see what AMD has in store with the brand new Radeon HD 4890...

The new Radeon HD 4890 is technically based on a new GPU design, which was formerly codenamed RV790, but fundamentally it is very similar to the RV770-based Radeon HD 4870. The two GPUs share the same feature set, same compliment of shader processors (800), texture units, and ROP configurations. Because we've covered the architectural details of the RV770 in a previous article, we won't do the same again here. If you'd like a little refresher, however, we'd recommended checking out our Radeon HD 4800 series launch article from last year. All of the details necessary to understand what's going on under the Radeon HD 4890's hood are in that article.

Although the features are technically very similar, the RV790 does differ from the RV770 in a number of ways. Some may be tempted to say the RV790 is simply an overclocked RV770, but that is not the case. The RV790 at the heart of the Radeon HD 4890 is a new chip that is comprised of more transistors than the RV770 (959M vs. 956M). The additional transistors are dedicated to updates made to the core to support higher clock speeds. According to AMD, the entire chip was re-timed and power distribution on the chip was altered. In addition, a decap ring--or ring of decoupling capacitors--was implemented around the chip to reduce signal noise. The changes to the core and the addition of the decap ring result in an increase in die and packaging size, but the end result is a GPU that can run at much higher clock speeds than the RV770.